1. Field of the Invention
The present invention relates to a radio communication system using portable cellular phone sets and radio communication terminal units (to be simply referred to as a portable cellular phone system hereinafter) which can perform data communication and, more particularly, to a portable cellular phone system with an automatic answering telephone function.
2. Description of the Prior Art
In a portable cellular phone system, an automatic answering telephone function (to be simply referred to as an automatic answering function hereinafter) is used when a callee cannot answer the phone or is outside the radio zone. Such an automatic answering function is generally installed on a network for a portable cellular phone system and managed by the management company (to be referred to as an automatic answering telephone center hereinafter) of the portable cellular phone system. In addition, a similar function is implemented by a memory mounted in a user's phone set itself (this function will be referred to as a built-in automatic answering function hereinafter). The former function has not much limitation in terms of recording time, but a memory must always be prepared, resulting in an increase in facility/running cost on the management company side. In addition, the user must access the automatic answering telephone center to hear the voice (message) recorded in the automatic answering telephone center. In general, the user is charged for the fee for a telephone call for this purpose. The latter function has limitations in terms of recording time, but the user can repeatedly play back the recorded message.
Under the circumstances, both the automatic answering telephone center scheme and the built-in automatic answering function scheme are generally prepared to allow a user to select one or both of the schemes.
According to the automatic answering function in the conventional automatic answering telephone center, a message is recorded in the automatic answering telephone center installed on a network, and the message is made to play back by connecting a general voice communication channel between the automatic answering telephone center and the terminal. For this reason, under a condition of poor communication quality, voice is interrupted or mixed with noise, resulting in deterioration in the clarity. As a consequence, the user must repeatedly play back the message. Naturally, in this case, the fee for a telephone call increases from the viewpoint of the user, and the communication traffic increases from the viewpoint of the management company.
In the conventional built-in automatic answering function scheme, when a caller connects to the portable cellular phone set of the callee, the phone set automatically plays back an answering message to allow the caller to store his/her message in the memory in the phone set itself. In this case, since the caller pays the charge for the telephone call, the user is charged no fee. If, however, the message is recorded under a condition of poor communication quality, the voice is recorded with low clarity. In this case, since the user cannot make out the message even after repetitive playback, he/she must call back the person who has left the message to inquire it.